Microwave Overloading my 3000W inverter

[WTrippe]

Hi,

So my generator quit working on me the other day. Until I can find some help to pull it out of my RV and change the starter I've been using my inverter.

I've got a 3000W GoPower pure sine wave inverter. 8x 6v AGM batteries wired as a 12V bank with around 1k AH. Everything is wired with 4/0 gauge wires.

It connects to a transfer switch along with the shore power cord. It also has a relay in there that shuts off the converter when the inverter is on.

It should surely be enough to run my microwave. It's only 800W or 1200W at most. I run the engine to compensate for the voltage drop.

When I try running the microwave the OUTPUT on my remote display maxes out and the inverter shuts off with the overload protection.

Any input is greatly appreciated.


Thanks,

William

[2oldman]

GordonThree wrote:
For me, the 12v decision was driven by a low price I found on the 2800 watt Magnum inverter I chose. The similar 48 volt model cost almost 2x as much.

Yah.. sometimes ya gotta pay to play! What I like is that I can run my air all day as long as I have a charging source helping out.

[GordonThree]

2oldman wrote:

GordonThree wrote:
fthe rather reliable technical manual for the 2800 watt inverter installed in my rv recommends DOUBLED four-ought for long runs.

That's nuts, which is why for consistent high-draw usage, higher voltage is recommended.

Agreed ... maybe next time!

For me, the 12v decision was driven by a low price I found on the 2800 watt Magnum inverter I chose. The similar 48 volt model cost almost 2x as much.

[BFL13]

"I'm using about 900W, 75A with it running and batteries holding at 12.4 V
remote display on the inverter is showing a 50% output which is too high."

The figures for the coffee maker are correct. There is nothing wrong with the inverter or the wiring. What is wrong is that 50% figure with only 75 amps being pulled. Should equate to about 7.5a 120v "output".

Then with the higher watt MW say at 150 amps draw or 15a 120V, the 50 gets to 100 on that remote and shuts things down. So that is what is broken--that "output" reading and shutdown triggered by it.

Also relates to that absurd 3a 120v "output" when the inverter is just in standby. The output reader gizmo is broken.

Can you get a new part to replace that broken thing or do you have to buy a whole new inverter? (If that, IMO get a simple inverter without such added gizmos) Or can you just by-pass that remote gizmo?

[time2roll]

Easy to measure the voltage at the inverter. However the inverter shuts down from overload NOT low voltage according to the OP.

I only see three possibilities:
1) there is some other load the OP is not aware of.
2) microwave is shot
3) inverter is shot (and this one bugs me because my GoPower has worked well for me)

[2oldman]

GordonThree wrote:
fthe rather reliable technical manual for the 2800 watt inverter installed in my rv recommends DOUBLED four-ought for long runs.

That's nuts, which is why for consistent high-draw usage, higher voltage is recommended.

[GordonThree]

four-ought cable is not the cure all either. the rather reliable technical manual for the 2800 watt inverter installed in my rv recommends DOUBLED four-ought for long runs. x2 on what Matt says, a run is round trip length, so 6ft cable is a 12ft run - often overlooked.

In my rig, the Highpoint micro with 1000 watt RF output, 1400 watt AC input reads 130 amps roughly on my inverter. who knows what the startup surge is, I don't have a peak-hold meter, but it could be double that number for a few milliseconds. I'm using 4/0 cable, about 7 feet total round trip, including the 4/0 cable links between each battery.

[Matt_Colie]

Ahboy,

When I did boat wiring upgrades, we ran into this all the time.

First, every wire table you can find easily is wrong. They all list the line loss as %drop. They tell what is good for 3% of 10%, and you should not even care about that. The key to the whole thing is voltage drop from the supply to the load along the PAIR of conductors. Many RV things use a frame ground. What is the equivalent wire size of that section of RV?? (Hint: Nobody actually knows) So, for any serious load, pull two conductors. I did not have to explain this with fiberglass boats.

That drop is very important because the entire life of a 12V nominal system exists between 12.6 and 12.0. That does not leave a lot of wiggle room to run an inverter for a microwave.

Now, the balance of the bank connection is another little jewel waiting to bite your big plan in the ass. First, lead acid batteries never play well in series, and if you have something 4 pair of GC2s, you have to pay a great deal of attention to balancing the connections and keeping them balanced as the age of the connections can change things. An variation of 0.01 Ohms in the connections will cause a voltage variation of 1.0V at 100A. There goes the inverter.

Yes, 4/0 is larger:
4/0 = 211600 Cm (Cm - Circular Mills 1/1000 In^2)
2/0 = 133100 Cm

That says that the conductivity of 2/0 is only 60% of 4/0, and as said, unless the inverter is as close to that bank as it can be, it will only get worse.

Matt

[MrWizard]

Fridge runs off the propane.
I started up the coffee maker without the engine running so I could see the draw.
I'm using about 900W, 75A with it running and batteries holding at 12.4 V
remote display on the inverter is showing a 50% output which is too high.

http://gpelectric.com/products/3000-watt-pure-sine-wave-inverter

3000W continuous, 6000W surge.

that is your clue
you need another meter, to verify the 75 amps load
either the inverter is drawing more,
or the control sensing circuit 'thinks' you are using more
so when you try to use the MW the controls module shuts you down
i think you are going to need to replace the inverter
is it still within warranty ?

[lawrosa]

hmmm... 1000 ah? Maybe the batts are sulfated. After all how and what is he charging them with? Those batts maybe never had the acid in them bubble even just a tiny bit.

I mean technically he can hit those batts with 300 amps. no? And at least 14.8 volts.

But we dont know. My guess the batts are dying a slow death from undercharging.

Test batts with hydrometer if not sealed.

That would be my guess.

Oh and yes... How you checked the water? Maybe a dead cell?

IO 4 gauge should be fine, but I run 2 gauge to my 1100 watt inverter and run/ran my micro @ 900 watts. And I have only 3 - 75 ah 12 volters....:E

[westend]

What is the "output" all about? Not following.

An output measurement on my inverter is in ACV. It also displays DCV input.
Are you referencing a battery monitor?

It might be easy to start from the device end of the chain. Connect the microwave into a different receptacle and see if it powers up. Don't mean to lead your diagnosis astray but with the type of receptacles installed in a typical RV (SCU) it's a wonder that more folks don't have trouble with them.

Good luck on the fix, it's probably something small.

[Isaac-1]

One other thing, what type of batteries are they, some deep cycle AGM are not rated for high discharge rate.

[GordonThree]

Could be something is simply wrong with the microwave, like a bad capacitor or problems with the windings on the transformer. On shore power, you have basically unlimited surge current for a few milliseconds, so a problem might not be evident until that unlimited source goes away.

[time2roll]

Try a hair dryer on low. Then step up the power slowly and see what goes.

[marcsbigfoot20b]

Only way to troubleshoot is to use an AC/DC amp clamp and measure how many amps are being used by the microwave vs how many amps are being pulled from the batteries.